Collection of examples for high performance computing at Yale University. This is a Yale-ified version of https://github.com/olmjo/tigress-scripts.

For information and support for high performance computing at Yale through the YCRC, see https://research.computing.yale.edu/.

This repository has a set of toy example scripts to help illustrate how your code can use and interact with the HPC resources and scheduling environment.

The focus is on R-based HPC, but there are examples with Python and MATLAB, too. All examples rely on Slurm. They can be adapted for other resource managers, but that's not included.

Each example can be used to submit a perfectly valid job that demonstrates certain aspects of computing in HPC environments. Even though they are toy, they should demonstrate certain features realistically enough to be useful.

The shell scripts with a .slurm suffix are SLURM scripts.

This is a bare bones example. It requests 1 task with 1 processor. It allows the scheduler to kill the job after 10 minutes. The script simply generates 1,000 random numbers using the Rscript interface to R.

To run under SLURM:

cd ./examples/ex00/
sbatch ex0.slurm

Go there!

This script represents a reasonable starting point for simple jobs. It is more explicit about how the job should be managed than Example 0.

• It still requests 1 task with 1 processor.
• It requests only 10 minutes of time.
• It uses a custom name in the queue and has both the error log and the output log merged into one file which begins with log.* and has a suffix determined by the job ID.
• It requests emails when it begins, ends, and aborts (the email address can be specified manually the defaults email the submitting user)

Every line beginning with # is just a scheduler directive. The remainder comprises an actual shell script. The script is verbose about where it is, when it starts, and what resources were given to it by the scheduler.

The script ultimately generates 1,000 random numbers using the Rscript interface to R.

This script includes all the reasonable defaults from Example 1. The only change is that it uses Rscript to run an external R script, which is how the job would usually be programmed.

The computational task in R is a copy of the example usage of ideal() from the R package pscl.

To run under SLURM:

cd ./examples/ex02/
sbatch ex2.slurm

Go there!

This job script uses the sample reasonable defaults from above, but it requests 3 tasks with 1 processor each. These tasks may land on the same physical node or not.

The R script uses an MPI backend to parallelize an R foreach loop across multiple nodes. A total of 3 * 1 = 3 processors will be used for this job (but 1 task is kept for the "master" process). When running the R script, we pass the value "10" as an unnamed argument. The R script then uses this value to determine how many iterations of the foreach loop to run.

Each iteration of the foreach loop simply pauses for 1 second and then returns some contextual information in a data.frame. This information includes where that MPI process is running and what it's "id" is.

To run under SLURM:

cd ./examples/ex03/
sbatch ex3.slurm

Go there!

This script now requests an array of jobs based on the template. For jobs in this array (indexed from 1 to 3), the shell script will run given the requested resources. Because the log file depends on the job ID, each of the three jobs will generate different log.* output.

Because R can read environmental variables we are able to use the index on an object of interest to us in R (e.g., a vector of names of files in a directory to be processed).

With this setup, each sub-job is requesting the same resources.

• 1 task with 1 core each

To run under SLURM:

cd ./examples/ex04/
sbatch ex4.slurm

Go there!

This script uses the default setup (see ex1), requests one task with 5 processors and runs a Matlab script. The Matlab script executes a loop sequentially and then in parallel where each of MC iterations takes MC/DUR seconds by design. The parallel loop (i.e., the one using the parfor construct) should be about PROCS times faster.

Unfortunately, this simple approach does not generalized to not generalize to parallel execution across nodes (with distributed memory).

cd ./examples/ex05/
sbatch ex5.sbatch

Go there!

This example is less a demonstration of features available (e.g., there is no use of job arrays or command line arguments) and, instead, shows a computational job that provides a reasonable template for many other embarrassingly parallel computational tasks.

Here, the goal is to use a non-parametric bootstrap to approximate the sampling distribution of correlation coefficients based on samples of size 25. The correlation of interest is between average undergraduate GPA and average LSAT scores among students at 82 different law schools.

The output generated from the R script is just the deciles from this distribution (without acceleration or bias-correction).

To run under SLURM:

cd ./examples/ex06/
sbatch ex6.slurm

Go there!

This example mirrors Example 6. However, it demonstrates use of a single task, where that task uses multiple cores.

To run under SLURM:

cd ./examples/ex07/
sbatch ex7.slurm

Go there!

This script uses the default setup (see Example 1), requests 5 processors on a single node, and runs a Python script.

The Python script executes a loop sequentially and then does the equivalent in parallel. Eeach of MC iterations takes MC/DUR seconds by construction. The map-based parallel evaluation should be about PROCS times faster. This approach does not generalize to multiple nodes.

cd ./examples/ex08/
sbatch ex8.slurm

Go there!

This script builds on the default setup (see Example 1), creates a job array with each task requiring 1 CPU.

This is a "hello world example" with Python just reporting out which job in the array it is and which node it is running on.

cd ./examples/ex09/
sbatch ex9.slurm

Go there!

This is a trivial demonstration of using a function provided from C++ through Rcpp. It verifies a sane development environment for C++-based R work.

cd ./examples/ex10/
sbatch ex10.slurm

Go there!

cd ./examples/ex11/
sbatch ex11.slurm

Go there!